Clonal relations among Salmonella enteritidis phage type 3 outbreak isolates traced by DNA fingerprinting

Isolates of Salmonella enteritidis PT3, a rare phage type, were recovered from patients and strains were isolated from an outbreak of gastroenteritis that occurred during the summer of 1997 in North-East Sardinia, Italy. To investigate possible clonal involvement in the outbreak and to evaluate the capacity to discriminate among S. enteritidis PT3 strains, a number of molecular typing methods including ribotyping with a mixture of PstI and SphI (PS-ribotyping), PFGE with endonuclease XbaI and RAPD typing with four arbitrary primers was used. The typical XbaI endonuclease generated PFGE pattern also explained the prevalence of highly clonal S. enteritidis PT3 strains in the outbreak and adjacent areas. RAPD fingerprinting with primers OPA 4, OPB 15, OPB17 and P1254 exhibited a single but unique RAPD profile among the outbreak strains from various sources that differed significantly from control strains. The results of this study showed that when an appropriately chosen set of primers is employed, RAPD fingerprinting can be used as an alternative, rapid, highly reproducible technique for tracing the clonal relations of S. enteritidis PT3, and can be more discriminatory than PFGE. Furthermore, this study revealed the possibility of PT3 causing outbreak.